1. Field of the Invention
The present invention relates generally to a plate fin type heat exchanger. More particularly, the present invention relates to a plate fin heat exchanger wherein the plate fins are disposed at an angle relative to the direction of air flowing through the heat exchanger.
2. Disclosure Information
A typical plate fin and tube type heat exchanger consists of a heat exchanger core having multiple tubes, or multiple rows of tubes, conveying a first heat exchange medium such as a refrigerant or coolant, with the tubes normally being perpendicular to the flow of a second heat exchange medium, such as air. The rows of tubes pass through multiple substantially parallel fins which are formed of thin plates of heat conducting material such as aluminum. The plates generally lie in planes substantially parallel to the airflow entering the front face of the heat exchanger. The fin plates may be flat or include some convolution portions slightly inclined to the direction of air flow.
As is well known in the heat exchanger art, the first heat exchange fluid flowing inside the tubes is used to heat or cool a second heat exchange fluid passing over fins external of the tubes. In the type of heat exchanger contemplated herein, the second heat exchange fluid is a gaseous medium and is normally air, so that the term "air side" is used herein to refer to the heat exchange between the fins and the second heat exchange fluid passing there over. The term "air" is intended to include both atmospheric air and other gaseous fluids acting as the second heat exchange medium. For a fin and tube heat exchanger, the overall heat transfer is largely controlled by the air side heat transfer coefficient and amount of effective air side heat transfer area. The air side heat transfer coefficient is largely controlled by the boundary layer growth along the fin.
As is further well known in the art, it has long been known to increase the air flow turbulence across the fin and reduce the boundary layer effect by striking louvres from the fin plates. Such louvres are taught in U.S. Pat. No. 5,062,475 wherein the louvres are chevron-shaped with one leg of the louvres lying in the plane of a fin convolution. The '475 patent teaches a plate fin wherein the louvres formed in localized corrugations have different leg lengths to provide increased air turbulence and reduced boundary layer effects. In such a design, the corrugation is localized and the height of the corrugation is limited by the thickness of the fin plate. Inasmuch as it is desirable to minimize the overall thickness of the fin plate, the overall height of the corrugation is somewhat limited.
Referring now to FIG. 1, a cross-sectional view of a typical chevron-shaped louvre corrugation is shown. As can be seen, the air flow through the louvres (indicated by A) can be somewhat tortuous resulting in an increase pressure buildup along the air side of the heat exchanger and ultimately a large pressure drop on the exit side of the heat exchanger. It would, therefore, be desirable to provide a plate fin design which allows the air entering the heat exchanger to strike a plurality of louvre front edges without turning or turbulating the air as it passes through the heat exchanger, resulting in decreased boundary layer effects and higher efficiency of the heat exchanger.
Therefore, it would be advantageous to provide a plate fin heat exchanger which reduces the pressure drop across the heat exchanger and improve its overall heat exchange effectiveness.